The present invention relates to an internal combustion engine control apparatus, and more particularly to an internal combustion engine control apparatus for controlling an idling operation condition of an automobile internal combustion engine.
In recent years, demands to reduce fuel consumption in an internal combustion engine to improve a cost-performance have been increasing more and more and the reduction of fuel consumption in an idling operation of the internal combustion engine has been studied from various points. For example, in order to reduce the fuel consumption in the idling operation, efforts have been made to reduce a mechanical friction of the internal combustion engine. Because of an improvement in machining precision and assembly precision for a friction surface of a cylinder of the internal combustion engine and use of a sliding member having a high boundary lubrication characteristic, a mechanical loss in a modern internal combustion engine has been significantly lowered compared to that of the prior art engine. After operation for a certain period, for example after a run of 500 km, the mechanical friction is further reduced compared to that at the time of shipment. In a certain automobile internal combustion engine, a suction pipe pressure in the idling operation is less than 200 mm Hg. In this manner, the rotation speed of the internal combustion engine in the idling operation has been lowered.
The reduction of the suction pipe pressure means the reduction of amount of suction air per cylinder of the internal combustion engine, and it causes the following problem.
As the amount of suction air per cylinder reduces, the operation enters a loss of ignition region in which combustion propagation is prevented and combustion is astable even if an air-to-fuel ratio is a theoretical one. In the loss of ignition region, a variation of an output torque of the internal combustion engine is large and the idling rotating speed is not stable. This imparts an uncomfortable feeling to a driver and finally may lead to loss of ignition.
It has been known that under a given suction pipe pressure, the higher the air-to-fuel ratio is, the less does the loss of ignition take place. In Japanese Examined Utility Model Publication No. 57-26035, the idling operation is detected from a time duration of a pulse signal applied to a fuel jet valve and decreasing the air-to-fuel ratio during the idling operation. In this method, since the air-to-fuel ratio is always lower during the idling operation, an exhaust gas condition is degraded and the fuel consumption rather increases.